ECSC collaborative elastic

Directorate-General For Research And Innovation

Description

Plastic fracture toughness testing and assessment methods
Industrial research and development

Sujets

• Sciences et techniques

Informations

• Publié par: DIRECTORATE-GENERAL-FOR-RESEARCH-AND-INNOVATION
• Nombre de lectures: 16
• Langue: English
• Poids de l'ouvrage: 39 Mo

Extrait

Commission of the European Communities
technical steel research
Properties and service performance
ECSC COLLABORATIVE ELASTIC-PLASTIC
FRACTURE TOUGHNESS TESTING AND
ASSESSMENT METHODS
Report
EUR 9552 EN
Blow-up from microfiche original Commission of the European Communities
technical steel research
Properties and service performance
ECSC COLLABORATIVE ELASTIC-PLASTIC
FRACTURE TOUGHNESS TESTING AND
ASSESSMENT METHODS
O.L TOWERS, S. WILLIAMS, J.D. HARRISON
THE WELDING INSTITUTE
Abington Hall n
GB-CAMBRIDGE CB1 6AL
Contract No 7210-KE/805
(1.9.1978 - 30.9.1982)
FINAL REPORT
Directorate-General
Science, Research and Development
1985 EUR 9552 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Market and Innovation
L-2920 LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of then is responsible for the use which might be made of
the following information
& ECSC-EEC-Euratom, Brussels- Luxembourg CONTENTS PAGE NUMBER
1. SUMMARY V.
2. NOMENCLATURE 3
3. INTRODUCTION 6
4. SCOPE OF PROGRAMME 10
4.1. Material Selection
4.2. Participating Laboratories 11.
4.3. Main Test Programme 12
5. MATERIAL CHARACTERISATION 13
5.1. Grade 281A to BS 1501: Part 2.
5.2. Grade 50D to BS 4360 16
5.3. Suitability of BS 4360-50D Material and 21
Selection of Main Programme Test
Temperatures
6. TEST SPECIMENS FOR MAIN TEST PROGRAMME 23.
6.1. Extraction of Specimen Blanks 23
6.2. Identification of Specimen Types 24.
7. TEST PROCEDURES 25
7.1. Specimen Preparation.
7.2. Testing and Reporting Procedures 27
8. DATA COLLECTION AND VALIDATION AT THE 30
WELDING INSTITUTE
8.1. Checking of Results and Problems Apparent 30.
8.2. Calculation of Fracture Toughness 32.
8.3. ICP Database: Description, Data Entry and 37
Checking
8.4. Assessment of Ductile Crack Growth and RCD 38.
Database
9. TEST RESULTS FOR MAIN PROGRAMME 40. IV
9.1. Data on ICP Database 40.
9.2. Data on RCD Database
9.3. Tension Test Results
9.4. K Values for Tests at -120°C. 40
10. ASSESSMENT OF TEST RESULTS 42.
10.1. Results of Control Sample Tests
10.2. Influence of Strain Rate and Loading Mode 45
10.3. Effects of Varying Overall Specimen Size 47.
10.4. Effects of Varying Individual Specimen 48.
Dimensions
10.5. Results for SENB Specimens Relative to CT 50.
10.6. Assessment of Large-Scale Tension Test 51.
Results
10.7. Resistance Curve Measurements and 60.
Estimation of Initiation Toughness
10.8. General Implications with Respect to Use 62
of EPFM
11. CONCLUSIONS 66.
12. ACKNOWLEDGEMENTS 70
14. REFERENCES 71
TABLES
FIGURES
APPENDICES ν
ECSC COLLABORATIVE ELASTIC-PLASTIC FRACTURE TOUGHNESS TESTING AND
ASSESSMENT METHODS
SUMMARY
A test programme has been carried out in 12 laboratories of 8
countries of the European Communities and 2 laboratories in Norway to
aid the understanding and assess the applicability of elastic-plastic
fracture mechanics (EPFM). This programme was carried out on a
ferritic structural steel, BS 4360-50D, using three 52mm thick plates.
Extensive characterisation tests were carried out to assess the basic
material properties and also to assess the steel's suitability for the
main test programme. These characterisation tests were, in fact,
repeated twice because a low alloy steel, Grade 281A to BS 1501: Part
2, was rejected as a result ofn tests, prior to the
selection and subsequent acceptance of the BS 4360-50D material.
Over 900 fracture toughness tests were carried out in the main
programme on the BS 4360-50D material in order to study the influences
of varying the following parameters:
(a) specimen configuration.
(b) overall specimen size
(c) individual specimen dimensions, e.g. crack length and specimen
thickness
(d) strain rate and type of control (i.e. load or displacement). VI
These studies were mainly performed at one temperature (-65°C) which
was selected to lie in the middle of the transition from ductile-to-
brittle behaviour with decreasing temperature. Tests were also-carried
out at room temperature, where crack growth always occurred by ductile
tearing, and at -120°C,e brittle cleavage fractures generally
occurred.
The data obtained from the studies have been entered onto computer
databases for convenience of analysis and to make the data available
for further analysis.
Analysis of the data indicates that the measured fracture toughness is
affected by the parameters studied by a different degree depending on
whether the fracture toughness corresponds to initiation of a cleavage
fracture or to ductile crack growth. For the tests at -65°C and
-120°C, where fracture generally occurred by a cleavage mechanism,
increases in overall specimen size, crack length, thickness or strain
rate tend to reduce the mean but not the minimum measured fracture
toughness. For crack growth by tearing, however, the measured
toughness values were relatively insensitive to changes in specimen
size, geometry and strain rate. These observations have important
implications with respect to the measurement of elastic-plastic
fracture parameters such as the J-integral or the CTOD. In particular,
it seems to be important to model the scale of the section thicknesses
in the structure if cleavage fracture is a possibility, and the
testing of full-thickness testpieces containing relatively large
cracks appears to be advisable.
A comparison between the results of tests on full-thickness wide plate
specimens loaded in tension and the measured fracture toughnesses in
full-thickness three point bend specimens was performed using four
current EPFM assessment routes, namely: the CTOD design curve, the J
design curve, the CEGB R6 procedure and the gross strain concept. It
was found that the assumptions concerning the appropriate applied
stress or strain to input into the design curves were important. It
was also apparent that the assessments using R6 were nearer to being
critical than those performed using the design curves, which is
consistent with the origins of these procedures. The results of
assessments made by the gross strain and the CTOD design curve
assessment methods were found to be consistent for a failure criterion
of 1 percent applied strain. VII
METHODES D'ESSAI ET D'EVALUATION, EN COLLABORATION AVEC LA CECA,
EN CE QUI CONCERNE LA RESILIENCE A LA FRACTURE ELASTO-PLASTIQUE
RESUME
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Un programme d'essais a été réalisé dans douze Laboratoires de huit
pays de La Communauté Européenne et deux Laboratoires en Norvège afin
de mieux comprendre et évaLuer L'appLicabiLité de La mécanique de La
rupture élasto-pLastique (EPFM). Ce programme a été réaLisé sur trois
pLaques de 52 mm d'épaisseur, en acier structureL ferritique de type
BS 4360-50D.
Un grand nombre d'essais de caractérisation ont été effectués afin
d'évaLuer Les propriétés matérieLLes fondamentales et également pour
déterminer si cet acier était utilisable pour le programme d'essai prin­
cipal. Ces essais de caractérisation ont, en fait, été effectués deux
fois, parce qu'un acier faiblement alLié, de nuance 281 A à BS 1501 :
deuxième partie, a été rejeté à La suite des essais de caractérisation
avant de choisir et d'accepter ultérieurement un acier du type
4360-50D.
Au cours du programme principal, iL a été procédé à pLus de 900 essais
de resilience sur le matériau BS 4360-50D afin d'étudier l'infLuence
de la variation des paramètres suivants:
a) configuration de Léchanti ILon;
b) taiLle générale de L'échanti ILon;
c) dimensions de chaque échanti ILon, par exemple la longueur des fissures
et l'épaisseur de L'échanti ILon;
d) taux d'alLongement et type de contrôle (par exemple charge ou dépla­
cement) /
Ces études ont été réalisées essentiellement à une température située
au milieu de la transition entre La ductiLité à la fragilité aux bas­
ses températures (soit -65° C). Des essais à température ambiante
ont également été réalisés, au cours desquels la croissance des fissu­
res était toujours due à une déchirure ductiLe, et à -120° C, où se pro­
duisaient généralement des fractures fragiles par clivage. VIII
Les données obtenues ont été introduites dans des banques de données
informatiques pour faciliter L'analyse et pour pouvoir en disposer
Lors d'analyses uLtérieures.
Une analyse des données montre que la rési Lienee mesurée est affectée
par Les paramètres étudiés dans une mesure vari